1. Field of the Invention
The present invention relates to a method and apparatus used in the completion of a well. More particularly, the invention relates to downhole tools. More particularly still, the present invention relates to downhole tools having an anchoring and sealing system.
2. Description of the Related Art
Hydrocarbon wells are typically formed with a central wellbore that is supported by steel casing. The casing lines a borehole formed in the earth during the drilling process. An annular area formed between the casing and the borehole is filled with cement to further support and form the wellbore. Typically, wells are completed by perforating the casing of the wellbore at selected depths where hydrocarbons are found. Hydrocarbons migrate from the formation through the perforations and into the wellbore where they are usually collected in a separate string of production tubing for transportation to the surface of the well.
Downhole tools with sealing systems are placed within the wellbore to isolate producing zones or to direct the flow of production fluids to the surface. Examples of sealing tools are plugs and packers. The sealing tools are usually constructed of cast iron, aluminum, or other drillable alloyed metals. The sealing tools typically contain a sealing system. The sealing system includes a sealing element that is typically made of a composite or elastomeric material that seals off an annulus within the wellbore to prevent the passage of fluids. The sealing element is compressed causing the sealing element to expand radially outward from the tool to sealingly engage a surrounding surface of the tubular. In one example, a bridge plug is placed within the casing to isolate upper and lower sections of production zones. By creating a pressure seal in the wellbore, bridge plugs allow pressurized fluids or solids to treat an isolated formation.
U.S. patent application Ser. No. 09/983,505, filed on Jun. 27, 2001 discloses a method and apparatus for a non-metallic sealing system, and is incorporated herein by reference in its entirety. In one aspect, the sealing element system defines a frac-plug used to seal a wellbore within the casing during a fracturing operation
FIG. 1 is a partial cross-section view of a plug from a pending patent application of the same assignee. The frac-plug 10 includes a sealing system 15 disposed around a mandrel 20. The sealing system 15 serves to seal an annular area between the frac-plug 10 and an inner wall of a casing (not shown) upon activation of the tool. The sealing system 15 includes a set support rings 65, 70 to contain a sealing element 95 upon activation of the frac-plug 10. The support rings 65, 70 are disposed on the mandrel 20 and located on the tapered surface of expansion rings 75, 80. The expansion rings 75, 80 fill in gaps that are created during the expansion of the sealing element 95. The sealing system 15 further provides inner cones 85, 90. The inner cones 85, 90 are disposed about the mandrel 20 adjacent each end of the sealing member 95. A tapered edge on the inner cones 85, 90 urge the expansion rings 75, 80 radially outward upon activation of the frac-plug 10.
The frac-plug 10 also has an anchoring system that includes a pair of cones 45, 50, a pair of slips 35, 40, a top ring 30 and a setting ring 25. Upon activation of the frac-plug 10, the cones 45, 50 are used to urge slips 35, 40 radially outward into contact with the surrounding casing, thereby securing the frac-plug 10 in the wellbore.
Typically, the frac-plug 10 is intended for temporary use and must be removed to access the wellbore there below. Rather than de-actuate the slips 35, 40 and bring the frac-plug 10 to the surface of the well, the frac-plug 10 is typically destroyed with a rotating milling or drilling device. As the mill contacts the tool, the tool is xe2x80x9cdrilled upxe2x80x9d or reduced to small pieces that are either washed out of the wellbore or simply left at the bottom of the wellbore. The more parts making up the tool, the longer the milling operation takes. In this manner, the use of cones 45, 50 increase the time required for the milling operation.
The frac-plug 10 is actuated by a separate setting tool (not shown). The setting tool is run into the hole with the frac-plug 10. The setting tool operates to set the frac-plug 10 by applying opposing forces to the inner mandrel 20 and the setting ring 30. In operation, the inner diameter of a setting tool straddles the top ring 25. The lower end of the setting tool abuts against setting ring 30. A force is applied to the setting tool from the surface causing the lower end of the setting tool to push axially downward against the setting ring 30. At the same time, the inner diameter of the tool pulls up on the mandrel 20. The opposing forces urge the slips 35, 40 to ride up cones 45, 50 allowing the outer portion of the slips 35, 40 to contact the inner surface of the casing. In turn, the expansion rings 75, 80 ride up the tapered surfaces of cones 85, 90, thereby causing the sealing member 95 to expand outwardly into contact with the casing. In this manner, the compressed sealing member 95 provides a fluid seal to prevent movement of fluids across the frac-plug 10 and the frac-plug 10 is anchored in the wellbore.
Like the frac-plug in the previous paragraph, conventional packers and bridge plugs typically comprise a sealing system located between upper and lower cone members. Packers are typically used to seal an annular area formed between two co-axially disposed tubulars within a wellbore. For example, packers may seal an annulus formed between the production tubing and the surrounding wellbore casing. Alternatively, packers may seal an annulus between the outside of a tubular and an unlined borehole. Routine uses of packers include the protection of casing from well and stimulation pressures, and the protection of the wellbore casing from corrosive fluids. Other common uses include the isolation of formations or leaks within a wellbore casing or multiple producing zones, thereby preventing the migration of fluid between zones.
One problem associated with conventional sealing systems of downhole tools arises when the tool is no longer needed to seal the wellbore, and must be removed from the well. For example, plugs and packers are sometimes intended to be temporary and must be removed to access the wellbore there below. Rather than de-actuate the tool and bring it to the surface of the well, the tool is typically destroyed with a rotating milling or drilling device. As the mill contacts the tool, the tool is xe2x80x9cdrilled upxe2x80x9d or reduced to small pieces that are either washed out of the wellbore or simply left at the bottom of the hole. The more parts making up the tool, the longer the milling operation takes. Longer milling time leads to an increase in wear and tear of the drill bit and additional expensive rig time. When the tool comprises of many parts, multiple trips in and out of the wellbore are required to replace worn out mills or drill bits.
Another problem associated with conventional metallic and non-metallic sealing systems is the manufacturing cost. Additional parts increase the cost and complexity of a tool.
There is a need, therefore, for a sealing system for use in a downhole tool that will minimize the time of a milling operation upon removal of the tool, and subsequently reduce the wear and tear on the drill bit. There is a further need for a sealing element with fewer components, thereby reducing the cost to manufacture. Still further, a need exists for a plug wherein the upper and lower cones have been removed.
The present invention generally relates to a method and apparatus for sealing a wellbore. In one aspect, the invention provides for an apparatus that is an anchoring and sealing system for use in a downhole tool. The anchoring and sealing system comprises of a compressible sealing member, a ring member at each end of the sealing member, and a slip member adjacent to each ring member. During activation of the anchoring and sealing system, the sealing member expands out and the slip member moves radially outward along an outer surface of the ring member into frictional contact with an adjacent surface of the wellbore, thereby supporting the expanding sealing member.
In another aspect, the invention provides for an apparatus that is a downhole sealing tool. As with the tool 10 of FIG. 1, the downhole tool comprises a body and an anchoring and sealing system disposed about the body. However, the tool of the present invention does not include upper and lower cones. Rather, support rings in the sealing and anchoring system are constructed and arranged to permit the radial expansion of a set of slips. In this manner, the manufacturing cost of the tool is reduced and the milling time to remove the tool from the wellbore is reduced.
A method is further provided for sealing an annulus in a wellbore. The method comprises running a tool into the wellbore, the tool comprising a sealing system having a sealing member disposed between a set of energizing rings, a set of expansion rings adjacent each set of energizing rings, a set of support rings, and a set of slips. The method further comprises activating the tool causing the sealing member to expand and the slip member to move radially outwards along an outer surface of the support rings, thereby supporting the expanding sealing member.